1. Field of the Invention
This invention relates generally to a brake booster and, more particularly, to a connecting mechanism for a power piston of a brake booster.
2. Description of the Prior Art
In the type of brake booster power piston that has two sections, a plastic-made central portion and metal-made disc portion, a problem has been encountered as to how to connect the two sections without having any relative movement therebetween and yet without having difficulty in connecting and disconnecting the same during the assembly and disassembly procedure of the brake booster.
Also known are brake boosters which have one-piece plastic power pistons shown, for example, in U.S. Pat. No. 3,938,424. However, plastic materials have been found to be weak, due to their nature, with respect to their resistance to destruction under high temperature. Brake boosters are disposed within the engine room of the vehicle and, therefore, the disc portion (i.e., 12b) of the power piston of this patent must be relatively thick for resistance to temperature if it is made of plastic even though such thickness is not necessary from a functional point of view. Thus, the increase in thickness of the disc portion causes an increase in the total weight of the booster itself. As compared with plastic, the inventor of the present invention has learned that metal plate will not be influenced due to the engine room temperature (about 70.degree. C. to 80.degree. C. maximum). Furthermore, the central portion of the piston in the present invention may be commonly used in any size of booster. Only the diameter of the metal portion in the present invention may be changed in accordance with the size of the booster used. This will result in a reduction in cost as compared to a conventional one-piece, plastic power piston as described hereinabove.